We propose to continue the investigation of the relation between distinct complex cognitive functions and scalp-recorded, non-stimulus-locked brain electrical activity. A first pilot study showed consistent EEG patterns in a group of 23 persons, which differentiated the performance of complex behavioral sequences over 60 sec. epochs, including reading, writing, and Koh's block design. In a pilot study 21 persons, more controlled tasks (motor activity eliminated, sensory differences minimized) engaged cognitive functions of spatial visualization, number facility and letter subsitution over 4-11 sec. epochs. In this study the decision rules differentiating pairs of tasks were consistent with previous results, but weaker. It is thus possible that previously reported research confounded cognitive differences with sensory, motor and arousal-related EEG patterns. In a series of 3 experiments we propose to amplify and isolate the basis of these relatively weak discriminations. If strongly discriminable, task-related EEG patterns, invariant across subjects, can be uncovered, we will then determine the extent to which sensory or other uncontrolled factors influence the discriminations by removing the stimuli during cognitive processing and by requiring the performance of differing cognitive operations from the same physical stimulus. "Task-load" will be controlled across tasks and between subjects, and behavioral and autonomic responses will be accurately assessed. Retest reliability, individual differences and effects of task difficulty will be studied. In each experiment, validity of the decision rules will be tested with previously unanalyzed data from approximately 50 additional subjects. Signal processing will be performed with the ADIEEG system which uses an anatomically-constrained multivariate pattern recognition algorithm to extract invariant EEG patterns.